From scrum lesson notes: 1. How and when grooming is done is decided by the Scrum TeamDoes it mean, PO, SM and Dev Team collaborate and decide when to schedule backlog grooming session? Or based on the requirement any one of them can schedule?

2. The Development Team is responsible for all estimatesIs above statement holds true for even release level estimates? My understanding is team is responsible for sprint level estimates. First time PO estimate PB at speculation phase and then PO along with the team in grooming session?

From scrum lesson notes:1. How and when grooming is done is decided by the Scrum TeamDoes it mean, PO, SM and Dev Team collaborate and decide when to schedule backlog grooming session? Or based on the requirement any one of them can schedule?

Yes your understanding is right, scrum does not provide any recommendation for running backlog refinement meeting. In general team does it as regular meeting , they do it mid sprint and discuss the upcoming stories at length and also estimate newly identified user stories.

2. The Development Team is responsible for all estimatesIs above statement holds true for even release level estimates? My understanding is team is responsible for sprint level estimates. First time PO estimate PB at speculation phase and then PO along with the team in grooming session?

Team is responsible for estimation, during speculation you may not have complete team but whoever is present participate in it, in general speculate phase only contains high level requirement, backlog will emerge when team starts working on it and during backlog refinement meeting team will participate in estimation. Unlike traditional projects where estimation is done only in beginning in agile we keep estimating the refined backlog items. So Team estimate the product backlog Items in story points and they also estimate detailed tasks in Sprint Planning meeting.